I monitor my rides using FitBit and Strava. I started out as a full-time road cyclist. However, I've recently begun gravel cycling. My primary purpose for cycling is fitness, in addition to enjoyment, fresh air, and exploration.
I've noticed that when I ride on dirt trails, I still feel like I am getting a great workout, but according to FitBit/Strava trackers, I expend less effort on trails. My hypothesis is that this is the case due to the rough terrain slowing me down, time spent having to navigate obstacles, etc... However, I do end up going up some of the toughest hills I've ever gone up on dirt, just not quite with the same level of momentum as I would on the road. I also know some friends who lost over 100 lbs strictly mountain biking.
So my question is, based on your knowledge, experience, and/or research, is there generally a significant calorie-burning difference between road and off-road cycling for a given time period?
What I mean by "for a given time period" is that, if I were to gravel cycle off-road for 2 hours versus ride on road for 2 hours, should I expect to generally burn less calories?
I add that constraint because obviously, if I were to gravel cycle off-road for 4 hours, I would likely burn more than if I road cycled for 2 hours. I'll add the caveat that cycling off-road opens up my opportunities and interests, so I may cycle for 1-2 more days than I would if I were limited to road-only, so even this comparison is not absolute in terms of overall fitness.